Fighting for the Cause of Allah (Jihaad)

Bukhari :: Book 4 :: Volume 52 :: Hadith 138

Narrated Anas:

I was in the company of Jabir bin 'Abdullah on a journey and he used to serve me though he was older than I. Jarir said, "I saw the Ansar doing a thing (i.e. showing great reverence to the Prophet ) for which I have vowed that whenever I meet any of them, I will serve him."